It's Because Of Gravity.

I humbly request an earth fun fact that will fill me with terror

Mount Everest is about as physically high as a mountain is capable of getting on our planet!

this damn thing sticks a little more than 29,000 feet up into the air, and is getting a couple of inches taller every year thanks to the two tectonic plates violently smushing their faces together right beneath it, but it won't ever get significantly higher up than it is now.

(which is still Too Damn High in my opinion)

"but buuuuuunjy," you wail dolefully, "mountains get higher than that on other planets! why can't WE have a 16-mile high volcano. buuuunjy. answer me." which is technically true! but it can't happen here, for one reason:

it's because of gravity.

see, it's kind of weird to think about because it's literally your house, but Earth is actually the largest rocky planet in the solar system by a WIDE margin!

sure, Mars can have a 16-mile-tall volcano, but Mars is about HALF the size of our dear old mama Gaia and its gravity is scaled to match. less gravity means that mountains have less downward pressure on them and so they can grow to much greater heights!

Olympus Mons is only as big as it is, because of WHERE it is.

which brings us back to our earthly neighbor, Everest!

unlike Mons up there, Mount Everest is fighting a brutal and ongoing war against the oppressive forces of Earth's gravitational pull, made even more complicated by those tectonic plates I mentioned way back at the beginning of this whole mess.

basically the breakdown of this three-way offensive is that the Indian-Australian tectonic plate is having a very slow head-on collision with the Eurasian tectonic place, shoving the Himalaya mountains (and our good ol' pal Everest) UP! but gravity is also shoving DOWN on the whole range, and past a certain point the mountains get too tall and the entire affair is just too big and heavy for the tectonic plate underneath it to hold it upright, and then the bottom of the plate starts to sink downward into the molten rock of Earth's Mantle!

think of it like stacking dogs on one of those floating pool lounge thingies- you can stack as many dogs on there as you like, but the float will just sink deeper and deeper in the water and your dog stack won't really get any higher.

though obviously, they are still all good boys.

it's like that!

so basically, Everest is about at the point where the tectonic plate beneath it is sinking at roughly the same rate the mountain is growing, so the whole thing is locked into equilibrium and will never get too much higher than it is now.

NEVER UNDERESTIMATE THE POWER OF A GOOD DOG METAPHOR.